A network switch creates a network among a plurality of end nodes, such as workstations, and other network switches connected thereto. Each end node is connected to one port of the network. The ports also serve to connect network switches together.
Each end node sends packets of data to the network switch which the switch then routes either to another of the end nodes connected thereto or to a network switch to which the destination end node is connected. In the latter case, the receiving network switch routes the packet to the destination end node.
Each network switch has to temporarily store the packets of data which it receives from the units (end node or network switch) connected to it while the switch determines how, when and through which port to retransmit the packets. Each packet can be transmitted to only one destination address (a “unleast” packet) or to more than one unit (a “multicast” or “broadcast” packet). For multicast and broadcast packets, the switch typically stores the packet only once and transmits multiple copies of the packet to some (multicast) or all (broadcast) of its ports. Once the packet has been transmitted to all of its destinations, it can be removed from the memory or written over.
Switching Ethernet Controllers (SECs) are network switches that implement the Ethernet switching protocol. According to the protocol, the Ethernet network (cabling and Ethernet ports) operates at 10 Megabits per second. Switches which operate at the desired speed of 10 Megabits per second are known as providing “full-wire” throughput.
In U.S. patent application Ser. No. 08/790,155, filed Jan. 28, 1997 now U.S. Pat. No. 5,923,660 which issued on Jul. 13, 1999, and incorporated herein by reference, in order to optimize through-put time, communication between SECs attempts to utilize the bus as little as possible so that the bus will be available as soon as a SEC wants to utilize it. Therefore, each SEC includes a write-only bus communication unit which transfers the packet out of the SEC by only writing to the bus. Thus, packets enter each SEC by having been written therein from other SECs and not by reading them in, since read operations utilize the bus for significant amounts of time compared to write operations. Having the bus available generally whenever a SEC needs it helps to provide the full-wire throughput.
However, when many SECs write to the same bus, the throughput is limited by the speed of the bus.